Method of image mensuration with selectively visible and invisible reseau grid marks

ABSTRACT

The method of this invention includes the steps of positioning a reseau with grid marks on the object and sequentially illuminating the grid marks separate from the object and illuminating the object separate from the grid marks or in a manner that the grid marks are not visible with the object. The image of the grid mark positions, when illuminated, are digitized and stored in computer memory and correlated with the image of the object when it is illuminated and digitized. The scale of the image can also be correlated to the scale of the grid marks.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to digital photogrammetric processes and morespecifically to a method of photogrammetric image mensuration in whichgrid marks can be provided, yet can be made invisible to an image of theobject to be mensurated and analyzed.

2. Background of the Invention

The photographic art for aerial surveillance, geological andarchaelogical study, mechanical, industrial, and architectural designand analysis, and other uses has become very well-developed over thepast several decades so that sharp, clear photographic images of theearth's surface and of objects on the earth's surface are obtainablefrom aerial photography, satellite photography, and the like. In fact,there already are in existence virtually countless aerial photographs infiles of national, state, and local government agencies, corporations,and individuals for purposes ranging widely from such things as militaryreconnaissance, surveillance and measurement of agricultural land andcrop conditions, monitoring municipal development and growth patterns,map making, geological assaying, land management, and the like.Additional photographing and re-photographing for subsequent comparisonwith previous conditions are being done on an increasing basis.

For many purposes, however, analysis of such photographic images cannotbe done by visual observation with sufficient accuracy or efficiency.For example, in spite of having exceptionally clear aerial photographicimages available, it may be quite impossible, even with accurate graphicinstruments and a magnifying glass, to measure the wing-span of anairplane parked on an airport apron, the square feet of pavement on allof the streets in a city, or the areas of potholes in a wetlandsinventory of a prairie.

Therefore, to improve their accuracy and efficiency, persons skilled inthe art of photogrammetry have found that computers can be a very usefultool for enhancing the photographic images or parts of the images and toaugment the analysis. To do so, the photographic image is converted intoa digital format that can be stored, processed, and displayed on acomputer controlled graphic display output, such as a cathode ray tube(CRT), hard copy printer, plotter, or the like.

A common method of converting a hard copy image to a digital array is touse a point sensor, such as a charge-coupled device (CCD), chargeinjection device (CID), or photodiode to scan the surface of the hardcopy and measure the light either transmitted through, or reflectedfrom, various points on the hard copy. The hard copy in this kind ofprocess is usually mounted on a rotating drum or on a flat table that ismovable in orthogonal X-Y directions. A large pixel array, such as a20,000 by 20,000 pixel area, can be acquired, which may, for example, bethe pixel array needed to represent the information on a 9"×9" (23 cm×23cm) film image, assuming individual pixels of about 12.5 μm diameter.

Some systems use a linear detector or sensor array, instead of a singlepoint sensor for the digital data acquisition. In such linear systems alarge number (e.g. 1750) of individual light sensitive elements aregrouped together in a linear row, and this linear array or row ofsensors is used to sweep scan a path over the surface of the hard copy.

Precise mechanical motion control is required for both the individualscan lines of a single point sensor and the groups of scan lines orsweep path of linear arrayed sensors in order to obtain a meaningful anduseable pixel array of the photogrammetric image. Such mechanicalaccuracy, while necessary for accurate pixel designation and resolution,cannot be obtained economically in the degree that would be required forresolution commensurate to pixel sizes of less than, for example, 50microns. Also, typical operations problems with such systems usuallyresult from inability to achieve and maintain the mechanical accuracyneeded over long periods of time. Consequently, the large data arraysrequired and the high cost to obtain the necessary mechanical accuracyhave kept the use of digital image processing of photographing images inlaboratories only and away from general commercial application and use.

In recent years, several manufacturers have made available semiconductorchips on which a plurality of CCD's or CID's are arranged in atwo-dimensional, rectangular array and mounted in a solid state camera,such as a "TM-540", manufactured by Puinix, of Sunnyvale, Calif. Thesesolid state cameras with rectangular sensor arrays can detect andmeasure light from a fixed frame or rectangular portion of the imagethat a person desires to digitize for computer use. When such camerasare used in conjunction with an analog to digital converter (sometimescalled a "frame grabber" device), the signal point or linear arrayscanning is no longer required to acquire a pixel array of digitalvalues for a photogrammetric computer image of a hard copy photograph,transparency, drawing, or the like. The physical spacings and sizes ofthe pixels are fixed by the geometric CCD or CID array and by themagnification of the hard copy image to the CCD or CID array.

These "frame grabbing" solid state cameras typically have rectangulararrays, such as, for example, about 510×492 CCD's or CID's. Whenproperly focused on an image, each CCD or CID in the array detects lightintensity from an individual spot or pixel area on the film image. Thus,a solid state camera that has an array of 510×492 CCD's on a rectangularchip will convert the portion of a film image within a focused frame toa square pixel array of 510×492, i.e., about 250,920 light intensitymeasurements or signals. Such an array of intensity measurements can, ofcourse, be recorded and displayed by a computer on a CRT in the samepixel array to provide a computer image reproduction of the portion ofthe film image within the focused or "grabbed frame". There has been arecent announcement by at least one manufacturer that a solid state CCDcamera with a 1,000×1,000 pixel array will soon be available, which willprovide larger "grabbed" frames, more accuracy, or a combination ofboth.

While the "frame grabbing" solid state cameras with rectangular CCD orCID arrays eliminate scanning, as described above, they are applicableonly where a limited size pixel array is needed. For example, such a"frame grabber" may be useful in focusing onto, and acquiring a digitalimage of, a particular small object, such as an airplane, that can beseen in an aerial photograph of a ten square kilometer area. However,they have not been useful before this invention for "grabbing" anddigitizing larger film image areas. In order to "grab" and digitize alarger film image area, the solid state camera had to be focused over alarger film area, thus sacrificing detail accuracy, since each pixelsize within the array also is focused over a larger area.

There are at least two products now available that can create a largepixel array by combining a "frame grabbing" two-dimensional image arraywith a scanning motion. In such systems, individual frames or sub-areasof larger macro-areas of film or paper photographs can be "grabbed" ordigitized and stored. Then, adjacent frames can be "grabbed" andpositioned correctly in the computer memory by either (1) moving the"frame grabbing" solid state camera very precisely to a predefinedadjacent position mechanically and then "grabbing" the pixel array forthat adjacent position, or (2) by moving the camera less precisely to"grab" the image at the adjacent location and relying on a preciselylocated grid mark or pattern of grid marks to geometrically relate one"grabbed" sub-area to the next "grabbed" sub-area. The "Autoset-1"manufactured by Geodetic Services Incorporated, of Melbourne, Florida isan example of the former of these techniques, and the "Rolleimetric RS",manufactured by Rollei Fototechnic GmbH, of Braunschweig, West Germany,is an example of the latter techniqe.

In general, reasonably priced opto-mechanical scanners have not beenable to achieve the accuracy considered to be necessary for many of thenewly-evolving applications. Scanners that could achieve high geometricresolution are slow and often force a user to resort to an off-linescanning process separate from the process of actually using andanalyzing the data.

Frame grabbing solid state camera systems, as described above, provide ahigher degree of accuracy within a small frame pixel array subarea.However, combining frame grabbing with scanning to get digital data overa larger macro-area again usually sacrifices accuracy for economy oreconomy for accuracy due to the need for highly accurate mechanicalposition control. The Rollei system mentioned above, and furtherdescribed in the West German patent no. DE 3428325, is considered to bea significant advancement in this regard by teaching the use of reseaugrids in combination with a "frame grabbing" solid state camera, but itstill requires manual identification of reseau grids or crosses. Also,the reseau crosses or grids are visible in the image and obliterate someof the contents of the photographic image where the grid marks arelocated. Also, the process of using a reseau in that manner is slow.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide a fast,accurate, yet relatively inexpensive image digitizing and mensurationsystem for analyzing hard copy photographic, transparency, paperdrawing, radar, and other images.

A more specific object of the present invention is to provide animproved mensuration frame grabbing system for digitizing and analyzinghard copy photographic, transparency, paper drawing, radar, and otherimages.

A still more specific object of the present invention is to provide animproved reseau grid for a mensuration frame grabbing system in whichthe reseau grid does not obscure or cover any part of the image and doesnot become a part of the image.

Another specific object of the present invention is to provide a framegrabbing digitizing mensuration system that uses a reseau grid locationreference system in which individual reseau detection and location isautomatic.

Still another specific object of this invention is to provide an imagedigitizing system in which one or more specific sub-areas of a largemacro-area image can be converted to digital format without having toconvert the entire macro-area image to digital format if not desired,thus avoiding the use of unnecessary computer storage and off-linecreation of a large pixel array and allowing mass storage of currentlyuninteresting image to be kept on film only, yet which also has thecapability of digitizing an entire large format macro-area image, ifdesired, in an efficient, accurate manner.

A further specific object of the present invention is to provide asystem that can quickly and accurately digitize a select feature shownin stereo photographs, correlate the digital images, and display them ina stereo image, such as a three-dimensional display or other stereooverlapping images, on a CRT, graphic display device, or the like.

A still further object of the present invention is to provide arelatively inexpensive, compact apparatus for digitizing and analyzinghard copy images in which all parts of a large hard copy image are keptvisible and stationary at all times.

Additional objects, advantages, and novel features of this invention areset forth in part in the description that follows, and in part willbecome apparent to those skilled in the art upon examination of thefollowing specification or may be learned by the practice of theinvention. The objects and advantages of the invention may be realizedand attained by means of the instrumentalities and in combinationsparticularly pointed out in the appended claims.

To achieve the foregoing and other objects and in accordance with thepurposes of the present invention, as embodimed and broadly describedherein, the method of this invention includes the steps of positioning areseau with grid marks on the object and sequentially illuminating thegrid marks separate from the object and illuminating the object separatefrom the grid marks or in a manner that the grid marks are not visiblewith the object. The image of the grid mark positions, when illuminated,are digitized and store in computer memory and correlated with the imageof the object when it is illuminated and digitized. The scale of theimage can also be correlated to the scale of the grid marks.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects of the present invention will become morereadily appreciated and understood from a consideration of the followingdetailed description of the preferred embodiment when taken togetherwith the accompanying drawings, in which:

FIG. 1 is a perspective view of the mensuration frame grabbing apparatusof the present invention with portions of the components cut away inseveral places to reveal the positions and structures of significantcomponents of the apparatus.

FIG. 2 is a front elevation view of the mensuration frame grabbingapparatus with portions of the structure cut away to reveal thepositions and structures of significant components.

FIG. 3 is a right side elevation view of the mensuration frame grabbingapparatus shown with several parts of the structure cut away to revealthe positions and structures of significant components.

FIG. 4 is a plan view of the mensuration frame grabbing apparatus of thepresent invention with portions of the structure cut away to reveal thepositions and structures of significant components.

FIG. 5 is a cross-sectional view taken along lines 5--5 of FIG. 4 toshow the components and structure of the double Z-axis drive apparatus;

FIG. 6 is a cross-sectional view taken along lines 6--6 of FIG. 2 toshow the reseau support structure and lighting components.

FIG. 7 is an enlarged view of the right side of the reseau supportapparatus and lighting components shown in FIG. 6 to illustrate thelighting functions of the components of this invention.

FIG. 8 is an enlarged cross-sectional view of the grid groove shown inFIG. 7 along with a plot of light intensity associated with the gridstructure;

FIG. 9 is an enlarged plan view of a computer image of the reseau gridof FIG. 8 according to the present invention.

FIG. 10 is an enlarged cross-sectional view of the grid of an alternateembodiment grid structure similar to that shown in FIG. 8 but modifiedto achieve an alternate grid image effect.

FIG. 11 is an enlarged plan view of a computer image of the reseau gridof FIG. 10 according to the present invention.

FIG. 12 is an enlarged cross-sectional view of still another alternateembodiment ink-filled grid mark according to this invention.

FIG. 13 is a block diagram of an axis position controller of the presentinvention;

FIG. 14 is a block diagram of the entire data information system of thepresent invention; and

FIG. 15 is an enlarged fragmentary view of a corner of the reseau plateand grid marks with an image frame shown at a home position and with analternate position image frame shown in broken lines and illustratingthe three coordinate systems of the present invention; and

FIG. 16 is a front elevation view of a CRT and cursor display of adigitized image according to the present invention;

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The mensuration frame grabbing apparatus 10 according to the presentinvention is comprised of a translation mounting structure in which asolid state camera 140 can be moved in orthogonal X, Y and Z directionsin relation to a reseau assembly 150. An object or image 176 to bedigitized for computer storage, manipulation, and analysis, such as aphotograph, map, film transparency, radar image, or the like can bemounted in the reseau assembly. The reseau assembly 150 includes areseau plate 160 that contains a plurality of grid mark grooves 162,preferably in the shape of crosses, which are utilized to mark andcoordinate spatial locations of the image on the object 176, as will bedescribed in more detail below. One of the significant features of thisinvention is the manner in which the grid mark grooves are created andutilized, as will be described in more detail below.

Referring now to FIGS. 1, 2, 3, and 4, the mensuration frame grabbingapparatus 10 has a superstructure frame or table 11 that is comprised offour upright corner members 12, 14, 16, and 18. The tops of these cornerframe members 12, 14, 16, 18 are connected together in a rectangularmanner by an elongated top front frame member 20, an elongated top rearframe member 24, an elongated top left side frame member 28, and anelongated top right side frame member 32. Similarly, the bottom ends ofthe corner frame members 12, 14, 16, 18 are connected together by anelongated bottom front frame member 22, an elongated rear bottom framemember 26, an elongated bottom left side frame member 30, and anelongated bottom right side frame member 34. This superstructure formsthe framework or table 11 on which the other operating components of theapparatus 10 are mounted. Footpads 36, 37, 38, 39 are provided under thecorners for supporting, leveling, and, if preferred, cushioning theapparatus from shock and vibration.

The top front frame member 30 and the top rear frame member 24 of thetable 11 described above also function as the X direction translationstructure for the camera carriage assembly 100, as will be described inmore detail below. A Y-axis translation platform assembly 50 issupported by the frame members 20,24 and provides the Y axis translationmounting for the camera carriage assembly 100. A double Z-axis mountingstructure 80 is mounted in the platform assembly 50, as will bedescribed in more detail below.

The camera carraige assembly 100 is mounted in the double Z-axismounting structure 80 in such a manner that it moves vertically upwardlyand downwardly in relation to the reseau assembly 150. Also, a lenscarriage assembly 120 is mounted on the camera carraige assembly 100within the double Z-axis mounting structure 80 in such a manner that italso is movable upwardly and downwardly in the Z-axis direction inrelation to the camera carriage assembly 100. As a result, when a solidstate camera 140 is mounted on the camera carriage assembly 100, and thelens assembly 142 is mounted on the lens carriage assembly 120, both thecamera 140 and the lens assembly 142 can be moved in unison upwardly anddownwardly in relation to the reseau assembly 150, or the lens assemblyitself can be moved upwardly and downwardly in the Z-axis direction inrelation to both the camera 140 and the reseau assembly 150, as desired.This double Z-axis translational ability allows optimum camerapositioning and lens focusing for achieving an optimum of desiredmagnification and high-quality transformation of selected parts of theimage on object 176 into digital data for computer storage,manipulation, recall, and display.

With continuing reference to FIGS. 1,2,3, and 4, the top front framemember 20 and the top rear frame member 24 are each fabricatedpreferably of elongated channel-shaped structures. An elongated trackwayor rail 40 is positioned substantially along the entire length on thetop surface of frame member 20. Likewise, a similar elongated rail ortrackway 42 is positioned along substantially the entire length on thetop surface of frame member 24. These trackways 40, 42 serve as thesupport surface for the platform assembly 50 in such a manner that theplatform assembly 50 can translate leftwardly and rightwardly in thedirection of the X-axis. The X-axis drive assembly 70 is positioned inthe channel-shaped frame member 20 and is connected to the platformassembly 50 as will be described in more detail below, for moving theplatform assembly 50 in a very controlled manner in the direction of theX-axis.

The platform assembly 50 has a rigid frame structure comprised ofelongated left side channel member 56 and elongated right side channelmember 58 connected together in spaced apart relation to each other byfront channel member 52 and rear channel member 54 to form a rigidrectangular frame structure. Cage guides 60, 62, 64, 66 are permanentlyaffixed under opposite corners of the rectangular frame structure ofplatform assembly 50 to support the platform assembly 50 in a confined,slideable manner on the trackways 40, 43. Specifically, the front cageguides 60,62 are slideably mounted on the front trackway 40, and therear cage guides 64,66 are slideably mounted on the rear trackway 42.These trackways and cage guides are configured in such a manner that theplatform assembly 50 can slide longitudinally leftwardly or rightwardlyin the direction of the X-axis, but it is constrained against movementin any other direction.

As best seen in FIG. 2, the X-axis drive assembly 70 is mounted in thechannel-shaped frame member 20. A bracket 79 is rigidly attached to theunderside of front frame member 52 of platform assembly 50 and extendsdownwardly to a position adjacent the channel member 20. A stepper motor72 mounted in the channel member 20 is connected by a coupler 73 to anelongated lead screw rod 76 that extends substantially along the lengthof channel member 20. The screw rod 76 is supported at each end byjournal bearings 74, 75, which are also attached to the inside of thechannel-shaped frame member 20. The screw rod 76 also extends throughand engages a ball nut 78 that is attached to the bracket 79. Therefore,when the screw rod 76 is turned in one direction by the stepper motor72, the ball nut 78 and bracket 79 pull the platform assembly 50 in onedirection along the X-axis, and when the stepper motor 72 turns thescrew rod 76 in the opposite direction, the platform assembly 50 islikewise moved in the opposite direction along the X-axis.

Referring again to all of FIGS. 1, 2, 3, and 4, it can be seen that thedouble Z-axis mounting structure 80 is positioned in the space betweenthe left and right frame members 56, 58 of platform assembly 50. Theprincipal structural component of the double Z-axis is preferably anelongated, rigid channel member 82, which provides a mounting structurefor a camera carriage assembly 100 and a lens carraige assembly 120,both of which will be described in more detail below.

As best seen in FIG. 5, in conjunction with FIGS. 1 and 4, the channelmember 82 of the double Z-axis mounting structure 80 is positionedbetween the left and right frame members 56, 58 in such a manner that itcan be moved or translated in the direction of the Y-axis. A pair ofangle iron brackets 84, 88 rigidly affixed to opposite sides of thechannel member 82 extend outwardly in opposite directions into thechannel frame members 56, 58 respectively. A pair of rails or trackways68, 69 are positioned over the angle iron brackets 84, 88 and affixed tothe respective top flanges of the channel frame members 56, 58. A leftcage guide 86 is affixed to the top flange of the angle iron bracket 84in a position to slideably engage the trackway 68. Likewise, a rightcage guide 89 is affixed to the top flange of angle iron bracket 88 in aposition to slideably engaged the trackway 69. Therefore, the doubleZ-axis mounting structure 80 is effectively suspended. from thetrackways 68, 69 in such a manner that it is slideably movable forwardlyand backwardly along the direction of the Y-axis, but is restrainedagainst movement in any other direction in relation to the platform 50.

The double Z-axis mounting structure 80 is moved back and forth in thedirection of the Y-axis by the Y-axis drive apparatus 90. This Y-axisdrive mechanism 90 is comprised of a stepper motor 92 connected to anelongated screw rod 96 by a coupling 93. The screw rod 96 is mounted inthe left channel frame member 56 of platform 50 by journal bearings 94,95 positioned respectively at opposite ends of the screw rod 96. Themidportion of the screw rod 96 passes through an ear 85 in bracket 84. Aball nut 98 in the ear 85 engages the threads of the screw rod 96 insuch a manner that rotational movement of the screw rod 96 moves thechannel member 82 of the double Z-axis mounting structure 80 along theY-axis. Therefore, actuation of the stepper motor 92 in one directioncauses the double Z-axis mounting structure 80 to move forwardly in theplatform 50, and actuation of the stepper motor 92 in the oppositedirection causes the double Z-axis mounting structure 80 to moverearwardly in the platform 50.

Referring now primarily to FIGS. 4 and 5, the double Z-axis mountingstructure 80 includes a camera carraige assembly 100 and a lens carriageassembly 120. Both the camera carriage assembly 100 and the lenscarriage assembly 120 have separate drive assemblies 110, 130,respectively, to move them upwardly and downwardly either together orsemi-independently in the direction of the Z-axis. Specifically, thecamera carriage assembly 100 is slideably mounted in the channel member82 in such a manner that it can be moved upwardly and downwardly in thedirection of the Z-axis by the camera assembly drive apparatus 110. Thelens carriage assembly 120 is slideably mounted on the camera carriageassembly 100 in such a manner that it can be moved upwardly anddownwardly in the direction of the Z-axis in relation to the cameracarriage assembly 100 by the lens carriage drive apparatus 130. Thesolid state camera 140 is mounted on the camera carriage assembly 100,and the lens assembly 142 is mounted on the lens carriage assembly 120.Therefore, the distance between the lens 142 and the camera 140 can beadjusted for desired magnification by actuating the lens carriage drivemechanism 130. Then, when the desired distance between the lens 142 andcamera 140 is attained, the entire assembly of the camera 140 and lens142 can be moved as a unit upwardly and downwardly in relation to thereseau assembly 150 for proper focusing.

The camera carriage assembly 100 is comprised of a vertically orientedplate 102 positioned in the channel member 82 with a horizontal cameramounting bracket 108 extending laterally outwardly from the plate 102. Apair of trackways 103, 104 are affixed to the inside surface of the webportion of channel member 82. Each of the trackways 103, 104 ispositioned in a vertical orientation and in parallel spaced apartrelation to each other. A pair of cage guides 106, 107 are affixed tothe plate 102 in positions where they slideably engage the trackways103, 104, respectively. Therefore, the plate 102 and camera mountingbracket 108 are movable upwardly and downwardly on the trackways 103,104, while being restrained against movement in any other direction inrelation to the channel member 82. The solid state camera 140 is mountedon the camera mounting plate 108 so that it also moves upwardly andownwardly along with the plate 102.

The camera carriage drive assembly 110 is comprised of a reversiblestepper motor 112 connected to an elongated screw rod 116 by a coupler113. The screw rod 116 extends through an ear 115 affixed to the plate102 where it is threadedly engaged by a ball nut 118 mounted in the ear115. A bearing block 114 attached to the channel member 82 supports thescrew rod 116. Therefore, actuation of the stepper motor 112 in onedirection moves the camera carriage assembly 100 upwardly, and actuationof the stepper motor 112 in the opposite direction moves the cameracarriage assembly 100 downwardly in relation to the channel member 82.

The lens carriage assembly 120 is comprised of a vertically orientedplate 122 positioned adjacent the forward surface of the plate 102 ofcamera carriage assembly 100. A horizontal shelf 128 extends outwardlyand laterally from the bottom edge of plate 122 to a position directlyunder the camera 140, and a brace member 129 helps to support the shelf128 in a rigid, nonmovable manner in relation to the plate 122. Anelongated trackway 124 is affixed in a vertical orientation to the frontface of plate 102. A cage guide 126 is affixed to the rear surface ofplate 122 in a position where it slideably engages the trackway 124.Therefore, the lens carriage assembly 120 is moveable upwardly anddownwardly on trackway 124 in relation to the plate 102, but it isrestrained from movement in any other direction in relation to plate102. The lens assembly 142 is mounted on the shelf 128 directly underthe camera 140 so that it also moves upwardly and downwardly along withthe lens carriage assembly 120 on the trackway 124.

The lens carriage drive assembly 130 is comprised of a reversiblestepper motor 132 mounted on the plate 102 and connected by coupler 133to an elongated screw rod 136. A journal bearing 134 attached to theplate 102 supports the screw rod 136. The screw rod 136 also extendsthrough a bracket 135 rigidly attached to the front face of plate 122. Aball nut 138 mounted in bracket 135 threadedly engages the screw rod136. Therefore, actuation of the stepper motor 132 in one directioncauses the lens carriage assembly 120 to move upwardly in relation tothe camera carriage assembly 100, and actuation of the stepper motor 132in the opposite direction causes the lens carriage assembly 120 to movedownwardly in relation to the camera carriage assembly 100. Anexpandable and contractable tubular envelope or light shroud 144 isshown attached at its upper end to the camera mounting bracket 108 andat its bottom end to the lnes shelf 128. This envelope 144 keepsextraneous light out of the optical path between the lens 142 and camera140.

Referring again to FIGS. 1 through 5, the reseau assembly 150 can bemounted by brackets 152, 153, or any other appropriate mountingstructure, to the frame members 22, 26 in such a manner that the reseauassembly 150 is positioned under the solid state camera 140 and lens142. Therefore, as can be appreciated from the description above, theX-axis drive assembly 70 and Y-axis drive assembly 90 can move thecamera 140 and lens 142 to any desired position over the reseau assembly150. Further, the camera carriage drive assembly 110 can move the camera140 and lens 142 in unison upwardly and downwardly in relation to thereseau assembly 150 as desired. Further, as described above, the lenscarriage drive assembly 130 can move the lens 142 upwardly anddownwardly in relation to the camera 100 as desired.

The reseau assembly 150 is best described by reference primarily to FIG.6 in combination with FIGS. 1, 3, and 4. A transparent object supportplate 172 is mounted horizontally in the lower fixed portion 156 of aframe 154. An object 176, such as a photograph, film transparency, map,or the like can be positioned on the upper surface of the object supportplate 172. A reseau plate 160 is then positioned directly on top of theobject 176 and clamped in place by the upper portion 155 of frame 154.The upper portion 155 of frame 154 is hinged to the bottom portion 156by a hinge assembly 157 to accommodate convenient removal of the reseauplate 160 and object 176 from the surface of the object support plate172. The reseau plate 160 includes a plurality of grid marks 162,preferably in the shape of crosses, in a precisioned measured patternonits bottom surface. The structures and usage of these grid marks 162will be described in more detail below.

A bottom light assembly 180 is positioned under the reseau assembly 150.This bottom light assembly 180 can be comprised of a plurality offluorescent bulbs 186 or other suitable light sources. The fluorescentbulbs 186 are shown mounted in sockets 184 attached to brackets 182.These bottom assembly lights include power and switch components (notshown) for turning the bottom lights on and off as desired. Atranslucent diffusion plate 174 is preferably positioned under theobject support plate 172 and mounted in lower portion 156 of frame 154.The diffusion plate 174 disperses light from the bottom light assemblyuniformly over the entire surface area of the object support plate 172.

As best shown in FIGS. 6 and 7, with secondary reference to FIG. 1, thereseau assembly 150 also includes a side light source preferably in theform of a fluorescent light tube 170 positioned in a trough 158 in thebottom section 156 of frame 154 and extending around the perimeter ofthe reseau plate 160. A light canal 159 in the form of a space betweenthe upper and lower sections 155, 156 of frame 154 allows light rays 190from the side light 170 to reach the edge of reseau plate 160.

A significant feature of this invention is the combination of thestructure of the grid marks 162 with the sidelights 170 to make the gridmarks visible or invisible as desired. Referring now to FIGS. 7 and 8,the preferred grid mark structure 162 of the present invention is in theform of a "+"-shaped groove precision etched into the bottom surface ofthe reseau plate 160. The bottom surface is preferred so that the gridmarks are positioned directly on the optical plane of the object 176,thus eliminating fuzziness due to focusing on the plane of the object.These etched grooves preferably have a generally trapezoidalcross-sectional configuration with generally inwardly slanted oppositesidewalls 162, 164 intersected by a generally flat top wall or surface165. The width of the open bottom of the groove is preferably in therange of 25 to 100 μm, and the depth of the groove is preferably in therange of about 2 to 10 μm.

Because of the shape of the groove of this reseau grid mark 162, asubstantial part of the light rays 190 directed horizontally through theplane of the transparent reseau plate 160 from the side lights 170 arereflected and refracted upwardly from the slanted sides 163, 164 of thereseau mark groove 162. The upwardly reflected and refracted light raysfrom the slanted surface 163 are indicated schematically in FIG. 8 aslight rays 191, 192. Likewise, the upwardly reflected and refractedlight rays from slanted surface 164 are indicated schematically as rays193, 194.

These upwardly directed light rays 191, 192 from slanted surface 163 andlight rays 193, 194 from the slanted surface 164 are directed into thelens 142 positioned over the surface of the reseau plate 160. The CCD orCID detectors in a rectangular array in the solid state camera 140 (notshown in FIGS. 7 and 8) can, of course, detect the spatial positions andintensities of these upwardly directed light rays 191, 192, 193, 194very accurately. particularly when the bottom lights 180 are turned offso that the only source of light is from the side light 170. As shown inFIG. 8, a plot 202 of light intensity in relation to spatial location onthe edge of a transverse plane cutting through the grid mark 162 as"seen" or detected by the solid state camera 140 results in two peakintensities 204, 206 spaced apart from each other in the same spatialdistance as the distance between the slanted sides 162, 164 of theetched reseau groove 162.

Such a solid state camera "view" in terms of light intensity can beconverted to digital data corresponding to specific pixel locations onthe surface of the reseau plate 160 for processing. The processing caninclude setting a threshold intensity 208 above which the peakintensities 204, 206 are recorded and stored by computer in correlationwith their spatial locations, and below which the intensities areignored. The resulting image recorded and stored in the computer,therefore, corresponds to the edges of the grid mark grooves 162. Theedge boundaries 195, 196 of the recorded peak 204 above the threshold208 can essentially correspond with the lateral extremities of theslanted surface 163 so that width between the boundary edges 195, 196represents the width 197 of the spatial location recorded on that sideof the reseau grid mark 162. Likewise, the edge boundaries 198, 199 ofthe peak 206 above the threshold 208 correspond generally with thelateral extremities of the slanted surface 164 and define the width 200in spatial location of that side of the grid mark 162. The resultingdata and computer memory therefore corresponds with the boundary linesof the grid mark 162, as illustrated in FIG. 9. As described above, theintensity peaks 204, 206 correspond with the grid mark boundary lines197, 200. Likewise, additional intensity peaks 228, 230, 232, 234, 236,238 correspond in spatial location with boundary lines 229, 231, 233,235, 237, 239, respectively, of the grid mark 162.

An alternate embodiment grid mark 162 is shown in FIG. 10. Thisalternate grid mark 162' is similar to the preferred embodiment gridmark 162 described above in that it is formed by etching a groove intothe bottom surface of the reseau plate 160. However, in this alternateembodiment grid mark 162', the side surfaces 163', 164' and the topsurface 165' are etched in such a manner that they are more rough andirregular instead of substantially smooth surfaces. Therefore, the lightrays 190 traveling longitudinally through the transparent reseau plate160 from the sidelights 170 are more scattered as they are reflected andrefracted generally upwardly through the top surface of the reseau plate160. For example, as illustrated in FIG. 10, the scattered generallyupwardly directed light rays 210 results from the longitudinal lightrays 190 incident on the right side 163' and top 165' of the etched gridmark 162'. Likewise, the generally upwardly directed scattered lightrays 212 result from the longitudinal light rays 190 incident on theright side 164' and top 165' of the grid mark 162'. As a result, thelight intensity "seen" or detected by the solid state camera 140 maystill have two spaced apart peaks 222, 224 generally corresponding inspatial location with the sides 163' 164' of grid mark 162', but theintensity 223 between the two peaks 222, 224 also remains substantiallyhigher than the background light intensity level 220. Therefore, thethreshold intensity level 226 can be set between the valley intensitylevel 223 and background intensity level 220. In this manner, therecorded spatial locations of pixels having light intensity greater thanthe threshold 226 is bounded by the edges 214, 215 corresponding to theentire width 216 of the grid mark 162'. The result, as shown in FIG. 11,is that the spatial conditions recorded by the solid state camera wherethe light intensity is above the threshold 226 corresponds with theentire width of the grid mark 162' showing as a broad line 216. Similarlight intensity levels at peaks 262, 264 and the valley 263 therebetweenabove the threshold 226 are recorded in the computer memory as the broadline 265 corresponding with the cross portion of the grid mark 162'.Consequently, the grid mark 162' stored in the computer memory as thefull width grid mark 162' rather than just the borderlines of the gridmark that were shown for the preferred embodiment 162 in FIG. 9.

An advantage of the grid marks 162 and 162' as described above is thatafter they have been recorded in the computer memory, they canessentially become invisible so as not to interfere with or block outany part of the image on the object film, transparency, or photograph176 as its image is being digitized and recorded in the computer memory.These grid marks 162 and 162' can be made invisible simply by turningoff the side light 170. Because the slanted sides 163, 164 are fairlysteep, there is virtuallyno noticeable interference with the light rays188 produced from the bottom light 180, as shown in FIG. 7, as thosebottom light rays 188 travel upwardly through the reseau plate 160 tothe camera lens 142. Therefore, after the object 176 is positioned onthe object support plate 172 and the reseau plate 160 is positioned ontop of the object 176, the whole assembly can be clamped into positionwith the top portion 155 of frame 154. Then, with the bottom lightassembly 180 turned off and the sidelights 170 turned on, the camera 140can be turned on to detect the precise position of the grid marks 162 or162'. This data corresponding with the positions of the grid marks 162or 162' is then sent to and stored in the computer memory. After thegrid mark positions have been recorded and stored in computer memory.the sidelights 170 are turned off and the bottom lights 180 are turnedon. With the sidelights 170 off and the bottom lights 180 on, the camera140 can be used to detect the light intensities of the bottom light rays188 allowed through the various parts of the object 176 as dictated bythe image thereon, which intensity data is then sent to the computerprocessed and put into computer memory as digital data correspondingwith the image on the object 176. As mentioned above, this datacorresponding with the image on the object 176 does not include the datacorresponding to the grid marks 162 or 162'. Therefore, the entire imagedetected from the object 176 is recorded in memory without any portionthereof being blocked out or interfered with by the grid marks 162 or162'. Yet the computer memory has stored therein data relating to theprecise spatial location of the grid marks 162 or 162' in relation tothe image from the object 176 for use in locating, scaling, measuring,analyzing, correlating, or displaying the image in precise terms.

Another alternative embodiment grid mark 162" according to the presentinvention is shown in FIG. 12. This alternative grid mark 162" is madeby etching a groove into the bottom surface of the reseau plate 160,similar to that described in the preferred embodiment grid mark 162shown in FIG. 8 above. However, in this alternate embodiment grid mark162", the groove is filled or partially filled with an opaque substance,such as ink 168. Therefore, the light rays 188 emanating from the bottomlighting system 180 cannot pass all the way through the reseau plate 160to reach the camera 140 where those light rays 188 are blocked by theopaque ink 168 in the grid mark 162".

Consequently, as shown by the plot 271 in FIG. 12, the intensity of thelight detected by the solid state camera falls off almost to zero, asindicated by the valley 272 in the plot 271 where the light rays 188 areblocked by the grid mark 162". The computer can be programmed,therefore, with a threshold intensity level 270 below which the computerwill recognize it as a grid mark. As a result, the spatial locationbetween the broken lines 273, 274 can be interpreted by the computer tocorrespond with the grid mark 162". While this alternate embodimentopaque grid mark 162" is functional, it has the disadvantage of alsoblocking out and making illegible any part of the image on the object176 that happens to lay just under the grid mark 162". Of course, thesidelights 170 are not required for use of this alternate embodimentgrid mark 162".

Three planar coordinate systems are used in association with mensurationoperations with the apparatus 10 according to this invention. Thesethree coordinate systems are illustrated in FIG. 15 in conjunction withthe reseau plate 160, grid marks 162, and a view frame 240 as "seen" bythe camera. First, there is a table coordinate system, indicated at 280,which is a measure or indication of the physical position or spatiallocation of the camera 140 and lens 142 on the X-axis and Y-axis inrelation to the table 11 and platform 50. Specific locations of thecamera 140 and lens 142 on this table grid system are indicated byeither (1) keeping track of stepper motor turns, which result inspecifically measured linear movement increments, or (2) locatordevices, such as electro-optic devices (not shown) mounted on thestructure. Second, there is the image coordinate system, indicated at282, which is a measure or indication of the spatial locations of partsof the image in relation to other parts of the image or to a benchmarkon the image. Specific locations on this image coordinate system 282 areprovided by the array of grid marks 162 on the reseau plate 160 asdiscussed above. Third, the frame coordinate system, indicated at 284,is a measure or indication of the locations of specific pixels of lightintensity within the frame "seen" by the solid state camera. Specificlocations of pixels in this frame coordinate system are indicated by thespecific CCD or CID light sensor element within the array of such lightsensor elements in the camera. As discussed above, typical chipscommonly used in solid state "frame grabbing" cameras have a pluralityof light sensor elements arranged in rectangular two-dimensional arraysof, for example, 510×492, although arrays of 1000×1000 light sensors arealso coming available. These three coordinate systems 280, 282, 284 areall synchronized and utilized together according to this invention, toachieve precise spatial integration and mensuration of parts or all ofthe image on an object 176. In addition, the position of the camera 140and lens 142 in the Z-axis is also integrated with these planarcoordinate systems for magnification and scale used in a particularoperation or image analysis.

As discussed above, the camera 140 and lens 142 are driven to desiredpositions in the X-Y plane on the table coordinate system by the X-axisdrive apparatus 70 and the Y-axis drive apparatus 90. The lens 142 isdriven upwardly and downwardly in the Z-axis direction in relation tothe camera 140 by the lens carriage drive assembly 130. The camera 140and lens 142 are driven in unison upwardly and downwardly in the Z-axisdirection by the lens carriage drive apparatus 110. Each of these driveapparatus 70, 90, 110, 130 has a stepper motor 72, 92, 112, 132,respectively, with an encoder mounted on each stepper motor to detectmotion of the respective motor shafts. An accurate record of rotationincrements of each stepper motor is available from each respectivestepper motor controller, which is a standard component of known steppermotor systems.

Each of these drive apparatus 70, 90, 110, 132 also has a home positionlocator or sensor to detect when the drive apparatus, thus the componentdriven in the X, Y, or Z axis, is in a "home" position. While these homeposition locators or sensors are not shown in the drawings, suchsensitive sensors as opto-interruptors and the like are well-known andreadily available items. For example, an LED and a photodiode can bemounted in spaced apart relation to each other on a frame member 20 ofthe table structure 11, and an opaque object can be mounted on theplatform 50 in alignment with the space between the LED and thephotovoltaic cell and adjusted so that it blocks the light from the LEDfrom reaching the photodiode when the "home" X-axis position of theplatform 50 is reached. The interruption of light is detected and can beprocessed to a "stop" signal in a manner known to persons skilled in theelectronics art for deactuating or turning off the stepper motor 72.Likewise such opto-electronic "home" position sensors can be mounted onthe platform 50 and channel member 82 for turning off the stepper motor92 when the Y-axis "home" position is reached, on the channel member 82and camera carriage assembly 100 for turning off stepper motor 112 whenthe camera Z-axis "home" position is reached, and on the camera carriageassembly 10 and the lens carriage assembly 120 for turning off steppermotor 132 when the lens Z-axis "home" position is reached.

An axis position controller system 350 is illustrated in the blockdiagram of FIG. 13. One of these controller systems 350 can be used foreach drive apparatus 70, 90, 110, 130. These axis position controllersystems 350 not only control the physical positions of the camera 140and lens 142 in the X, Y, and Z axes, but they also provide the spatiallocation and magnification data to the computer system 100for use alongwith the pixel position and light intensity data from the solid statecamera 140 in mensuration and image display functions.

A block diagram of a control system 310 called "CPRIME" according tothis invention interfaced with a VAX 11/780 computer system 300 is shownin FIG. 14. This operator system 310 for the mensuration frame grabbingapparatus 10 includes four axis position controller systems 350, such asthat shown in FIG. 13--one for each drive system. For convenience indescribing this control system 310, the X-axis controller system isdesignated 351, the Y-axis controller system is designated 352, thecamera Z-axis controller system is designated 354. Thus, the X-axiscontroller system 351 controls the X-axis drive 70, the Y-axiscontroller system 352 controls the Y-axis drive 90, the camera Z-axiscontroller system 353, controls the camera carriage drive 110, and thelens Z-axis controller system controls the lens shelf drive 130. Astandard interface 312, such as an RS-232C interface, is provided toconnect the terminal drive 306 of computer 300 to the controllers 351,352, 353, 354 via the address bus 314, control bus 316, and data bus318. The camera 140 is connected through a CDAX switch 320 to the framegrab ber analog-to-digital converter 304, such as a Gould FD- 3000(trademark), can be a component of the computer system 100. An operatorstation 302, preferably comprising a keyboard and a CRT or graphicaldisplay device, is also connected to the terminal driver 306 of thecomputer 306.

As mentioned above, where stereo mensuration or comparator mensurationis desired, two twin mensuration frame grabbing systems 10 according tothe present invention are used. The second of the twin system 500 is notillustrated in detail because it can be essentially identical to themensuration frame grabbing system 10 described in detail above. However,the control system 510 for the twin mensuration frame grabber system 10is shown in the schematic diagram of FIG. 14 tied into the computersystem 100 in the stereo embodiment according to this invention.Specifically, the control system 510 of the twin mensuration framegrabbing system 500 is shown in FIG. 14 much the same as the controlsystem 310 of the mensuration frame grabbing 10. It includes four axiscontrollers, an X-axis controller 551, a Y-axis controller 552, and alens Z-axis controller 554, for controlling the corresponding X-axi,Y-axis, camera carriage, and lens shelf drives (not shown) of the twinmensuration frame grabbing system 500. An interface 512 connects thecontrollers 551, 552, 553, 554, via address bus 514, control bus 516,and data bus 518 to the terminal driver 306 of computer 300. Also, thesolid state camera 540 of the twin mensuration frame grabbing system 500is connected to the frame grabber A/D converter 304 through the CDAXswitch 320.

In order to obtain meaningful data from the mensuration frame grabbingsystem, it is necessary to orient the image with the table coordinatesystem. This initializing or "inner orientation" is accomplished afterthe object 176 and reseau plate 160 are loaded in the frame 154 andmounted in the table 11 by allowing the camera to seek its "home"position as defined by the opto-interrupter limit sensors mounted on thestructure as described above. This "home" position in the X-Y planeestablishes a zero point on the table coordinate system in the X and Yaxes.

In stereo mensuration, the bottom lights 180 are switched on and theside lights 170 are initially switched off as the camera 140 of one ofthe twin mensuration frame grabbing systems 10 is driven in the monomode by drives 70, 90 over its respective reseau assembly 150 until itis focused on the desired photo or other image area of the respectiveobject 176. As the camera 140 moves, it grabs a frame of a portion ofthe image about every 1/30th of a second. These image frames areconstantly viewable on the computer CRT 302, so the operator can seewhen the camera 140 is focused on the desired image area on the object176.

Once the camera 140 of the first frame grabbing apparatus is focused onthe desired image area, that image is grabbed and stored in computermemory and displayed on the CRT of the operator station 302. Then thebottom lights of the other of the twin mensuration frame grabbingsystems 500 are turned on, and the camera of the system 500 isdrivenover its respective reseau assembly, which contains the photographor other hard copy image that is the stereo conjugate of the photographor other hard copy image that is mounted in the reseau assembly of thefirst system 10 until the camera of the second system 500 is focused onthe corresponding image area. During this process, the digital data ofimage frames grabbed by the twin system 500 is merged by the computerand displayed together with the computer stored image grabbed by thefirst system 10. In this manner, stereo parallax removal from the twoconjugate stereo images can be accomplished easily and precisely by theoperator viewing the superimposed conjugate images, in spite of thesomewhat less precise mechanical positioning information available fromstepped increments of the respective axis drives. In other words, whilethe respective cameras 140, 540 of the twin mensuration frame grabbingsystems 10, 500 can be driven to about the same positions, eitherseparately or concurrently, to the desired image area of the conjugatefilms to be viewed and analyzed, the precise conjugate position of thesecond camera 540 over the desired image area on the film in relation tothe position of the first camera 140 does not have to be accomplished byprecise placement of the respective conjugate films in the respectiveframe grabbing apparatus 10, 500 or by precisely coordinated andmeasured movement of the respective cameras 140, 540 to those conjugateareas of the films. Further, stereo-parallax removal does not have to beaccomplished by the common, but slow and cumbersome method of shiftingone of the images by software and rewriting it to the display, which isfar too slow for real-time stereo-parallax removal. Instead,stereo-parallax removal is accomplished according to the presentinvention by hardware scroll, i.e., moving the second camera 540 inrelation to the image of the desired area grabbed by the first system 10and stored in computer 100 as both this stored image from the firstsystem 10 and the image from the scrolling second camera 540 aredisplayed together superimposed on each other. In this manner, theoperator can see on the CRT precisely when the conjugate image areas onthe respective films or other objects on each of the two mensurationframe grabbing apparatus 10, 500 come together in a precise, sharplyfocused, stereo image.

When both of the cameras are stopped on the desired stereo-viewable pairof conjugate images, the bottom lights 180 are turned off for a shorttime, so there is no film illumination. Simultaneously, the side lights170 are turned on for grid illumination. With the side lights 170 on,each camera 140 "grabs" a frame at the location where it was stopped,thus grabbing an image of the grid marks 162 within the frame "seen" bythe camera 140. Each camera 140 feeds that "grabbed" image of the gridmarks 162 to the computer. The computer can discern the specific spatiallocations of the grid marks 162 in the frame coordinate system by thespecific pixels or CCD light sensors in the CCD array in the camera 140that sense the grid marks 162. Therefore, the grid marks 162 areautomatically located within the frame and frame coordinates arecomputed. These frame coordinates are then used to compute coefficientsof transformation for transforming the spatial locations of the gridmarks 162 within the "grabbed" frame to table coordinates in relation tothe "home" position using the known table coordinates of the grid marks.Thereafter, the grid marks 162 provide the image coordinate system sothat any portion of the object 176 image within a "grabbed" frame thatincludes any grid marks 162 can be located in precise spatialorientation to other image portions "grabbed" or to the "home" position.The spatial measurements of subsequent camera 140 movements by theencoder input and direction sensing logic shown in FIG. 13 need only beaccurate enough for the microprocessor to determine which grid marks 162are within the subsequent "grabbed" frames.

Since the sizes and distances between all the grid marks 162 etched intothe reseau plate 160 are known very precisely and are also fed into thecomputer, the computer can precisely check and adjust the exact spatiallocations of grid marks 162 in the subsequently "grabbed" frames to thegrid marks 162 in previously "grabbed" frames or to the "home" position.In other words, using the coefficients of transformation and the knowntable coordinates of the grid marks 162, the image coordinates andsegments "grabbed" can be related geometrically to the table coordinatesystem.

After the image of the grid marks 162 within the "grabbed" frame foreach camera 140, 540 are stored in computer memory, as described above,the side lights 170 are turned off, and the bottom lights 180 are turnedback on. Then, without moving the cameras 140, 540 the same framepositions are "grabbed" again, this time "grabbing" the portion of theobject 176 image within the frame. This image within the frame "grabbed"by each camera 140, 540 is also sent to the computer 100 with eachfeature of the image "grabbed" being sensed in pixels by light intensityfocused on individual CCD light sensors in the CCD array of each of thecameras 140, 540. Therefore, each camera 140, 540 feeds two images tothe computer 100 for each frame position, i.e., the grid mark 162 imagewithin the frame and the portion of the object 176, image within theframe. Since the cameras 140, 540 do not move between "grabbing" thesetwo images, the grid marks 162 are in computer memory in precise spatialposition on the "grabbed" segment of the object 176 image. However,since they were "grabbed" separately, first one and then the other, thegrid marks 162 to not block out or distort any part of the object image.

If the system has been initialized properly, as described above, such asby observation of a benchmark or even the film edge, the tablecoordinates can be transformed into film or image coordinates. Forexample, as illustrated in FIG. 15, if a frame 240 was "grabbed" at the"home" position, illustrated by dot 242 in the center of the frame 240,five grid marks 162 are "grabbed" in the frame 240. Each of those gridmarks 162 are recognizable by the computer as being the grid marks 162expected to be in a frame "grabbed" at "home" position 242 by thegeneral positioning of the reseau plate 160 in the table 11. Even if thereseau plate 160 is not placed precisely in the same place each time, itis close enough if it is placed so at least the same reseau grid marks162 can be captured within a frame "grabbed" at "home" position 242.This is not to say that a frame has to be "grabbed" at "home" positioneach time the apparatus 10 is initialized, but it could be used as acheck on proper reseau plate 160 positioning. As long as the reseauplate 160 is positioned each time close enough that the same grid marks162 would be in the frame "grabbed" at "home" position if such a framewas "grabbed", spatial positions can be taken from any other grid marks162 that appear in any other frame "grabbed" over other parts of thereseau plate 160, because the spacings and sizes of all the grid mark162 on the reseau plate 160 are known precisely.

To illustrate further, the four grid marks 162 "grabbed" in frame 240 at"home" position 242 in FIG. 15 are not shown exactly centered in theframe 242. However, since the camera 140 is centered on the "home"position 240 and the frame coordinate system is fixed by the CCD arrayin the camera, the actual pixels in which the five grid marks 162 inframe 240 can be fed to the computer 100, and a correction factor can bedetermined to "adjust" the positions of the grid marks 162 by softwareto ideal positions as if they were centered exactly around the "home"position 242, i.e., initializing the image coordinate system to thetable coordinate system. Then, when the camera 140 is moved by steppermotors 72, 92 to an alternate position and a frame 240' is grabbed atthat alternate position, the encoders of the stepper motors, 72, 92,along with the logic illustrated in FIG. 13, will keep track ofdistances and directions the camera 140 is moved. By correlating thosedistances and directions with the known spatial settings of the gridmarks 162 on the reseau plate 160 and keeping track of each such gridmark 162, e.g., by sequential (i,j) numbers in a cartesian coordinatesystem, and by applying the correction factor determined above, thecomputer will know or recognize which grid marks 162 show up in theimage "grabbed" in the alternate frame 240'. Since the (i,j) imagecoordinator of those grid marks 162 within alternate frame 240' areknown along with their precise spatial position from "home" position,the computer can further correct or update actual table coordinates andpixel locations in relation to the image coordinates at that alternate"grabbed" frame 240' location. Therefore, when the side light 170illumination of grid marks 162 is turned off and the bottom light 180 isturned on, the image segment "seen" by the camera 140 can be loadedprecisely in spatial relation to any other "grabbed" image segment.

Also, once the stereo initialization is completed, the cameras 140, 540can be moved over the two conjugate images, respectively, and, uponstopping the cameras 140, 540 over a desired image segment, proper tableand image coordinates for each pixel of the image segment can beobtained as described above so that stress-free stereo observation isfeasible. Then, mensuration of image points can be done with a movablecursor in the digital image display. The image display is fixed orfrozen in a desired scale, and the cursor movement is scaled tocorrespond with the scale of the image. As the cursor is moved over thefrozen image the distances moved to scale can be displayed.

The mono-comparator mode of operation differs from the stereomensuration mode described above only in that a single mensuration framegrabber apparatus 10 is used instead of two of them. The purpose of themono-comparator mode is to create image coordinates of features that aredesired to be analyzed or measured. A movable cursor can be used topoint to specific points or features in a fixed or frozen image segment"grabbed" by the camera 140 and for mensuration of features in theimage. The cursor can be moved manually or by automatic sweep to atarget feature using pattern recognition. Transformation of pixel orframe coordinates into table coordinates and further into imagecoordinates is based on the reseau grid marks 162 and their automaticdetection as soon as the camera 140 stops in the same way as describedabove for the stereo mensuration mode. This procedure is applicable atany of the available magnifications.

The comparator cursor movement in the CRT display window and the cameramovement are smoothly controlled and coordinated according to thisinvention in such a manner that the cursor can be moved within a displaywindow on the CRT of the grabbed image by appropriate user controls andwhen the cursor reaches an edge of the display window, the X-axis andY-axis drives 70, 90 start to drive the camera 140 over the film orobject 176 as the CRT simultaneously displays real-time video scrollimages as the camera 140 moves. In other words, as illustrated in FIG.16, the computer-generated cursor 250 is movable by the operator in anyX or Y direction within the display window 252 of a CRT 254. Suchmovement can be controlled by a joystick switch, omni-directional ballswitch (commonly called a "mouse"), designated keys on a keyboard at theoperator station, or the like. Such cursor control switch devices arewell-known in the computer art and need not be described in detail here.When the cursor 250 is moved to display window limit or margin, such asthe right margin 256, the X-axis controller 351 actuates the X-axisdrive 70 to move the camera 140 to the right. As the camera 140 moves tothe right, it grabs images about every 1/30th of a second andcontinuously displays those images in a real-time scroll over the filmor object 176 until the camera reaches the desired spot and the CRT 254displays the desired image. The joystick or other control switch canthen be manipulated to move the cursor away from the margin 256 and backinto the display, at which time the controller 351 deactuates the drive70 and stops the movement or translation of the camera.

Of course, movement of the cursor into other margins causes the camerato move or scroll in other directions. For example, movement of thecursor 250 to the left margin 257 actuates X-axis drive 70 to movecamera 140 to the left. Likewise, movement of the cursor 250 to eitherthe top margin 258 or the bottom margin 259 actuates the Y-axis drive tomove the motor in those respective Y-axis directions.

When the camera 140, is positioned to display the desired image, theside lights 170 are flashed to capture the grid image, the precisecamera orientation with respect to grid marks 162 are determined andcalibrated, as described above, and the cursor position can becalibrated to grid marks 162. Therefore, the cursor position coordinatescan also be displayed. This operation can be programmed to occur uponpressing a designated "select" button or key on the keyboard (notshown). Succeeding cursor position coordinates calibrated to the scaleand magnification of the image display can be used in making precisemeasurements of objects or spatial relationships in the display.

The above-described motion and display sequence appears on the displayCRT 254 as a smooth operation, without spatial jumps in the courselocation or in successive image display during scrolling. It is alsodone quite conveniently with a minimum of operator controls or specialtraining.

This frame grabbing apparatus 10 can also be used to build up and storea large pixel array. For example, if an entire 20"×10" (50 cm×25 cm)film image needs to be digitized and stored, a series of adjacent framesof the image and reseau grid marks 162 can be grab bed, coordinated toone precise table and then to a precise composite image coordinatesystem, and then stored in computer memory. Such a 20"×10" (50 cm×25 cm)image may require an array of 40,000×10,000 pixels of 12.5 μm diameter.Since a solid state camera 140 that grabs an array of only about 510×492pixels in its frame may cover only a fraction of the entire image, thegoal is to "grab" a number of adjacent frames, e.g., of about 510×492pixels and piece or mosaic, i.e., "file", them together to obtain theentire 40,000×20,000 pixel array of the whole image.

This goal can be achieved according to the present invention bysequentially stopping the camera 140 in a synthetic raster pattern undersoftware control and "grabbing" adjacent frame segments of the imagealong with the grid marks 162 on those segments in the respectiveframes. Then, using the grid marks 162 and image coordinates, theindividual frame data can be merged, i.e., "filed", together andconverted into digital data for the entire 20"×10" (50 cm×25 cm) image.In the example described above, a mosaic comprised of about 80×40 framesof 510×492 pixels apiece would be required for the 40,000×20,000 pixelarray of the entire object image.

Another use of the mensuration frame grabbing apparatus 10,500 of thepresent invention is to provide joint analysis and manipulation ofseparate, but related, image data sets. For example, it might bedesirable to compare an older photo or map of an area with a more recentone, perhaps to detect changes or to update available information orimages. Such an operation could be conducted in much the same manner asthe stereo mensuration operation described above, except that an oldimage and a new image would be mounted in two separate mensuration framegrabbing apparatus 10,500, instead of two concurrently photographedimages at different angles. Difference or changes between the old andnew images can be detected visually on the CRT, or a computer could beprogrammed to detect such changes automatically.

As mentioned above, the lens 142 and camera 140 combination has avariable magnification capability under manual or computer control. Suchvariable magnification preferably covers a range of about 12.5 μm pixelsto 125 μm pixels and still maintain the same logic of operation withautomatic recognition of reseau grid marks 162 and automatictransformation of frame coordinates into table and image coordinates. Todo so, the reseau plate 160 is designed preferably so that at maximummagnification with the smallest pixel size of about 12.5 μm, there willbe five reseau grid marks 162 in each frame or field of view of thecamera 140. Also, at minimum magnification with about 125 μm diameterpixels, the reseau grid marks 162 and their spatial locations still haveto be recognizable. The grid marks 162 having generally trapezoidalcross-sections etched into the bottom of the reseau plate 160 asdescribed above are most appropriate for this purpose.

The foregoing description is considered as illustrative only of theprinciples of the invention. Further, since numerous modifications andchanges will readily occur to those skilled in the art, it is notdesired to limit the invention to the exact construction and operationshown and described, and accordingly all suitable modifications andequivalents may be resorted to falling within the scope of the inventionas defined by the claims which follow.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:
 1. The method of imagemensuration, comprising the steps of:positioning a reseau with preciselyspaced grid marks thereon on an exposed surface of an object containingthe image and under a solid state camera that is capable of convertingilluminated images to digital data; illuminating the reseau grid marksand digitizing the image of the grid marks within the camera's view withthe object image not illuminated, and storing the digitized data,including spatial location, of the grid marks in a computer memory;removing the grid marks from the capability of the solid state camera toview them; illuminating the object image and digitizing the object imagewithin the camera's view, and storing the digitized data of the objectimage in a computer memory; correlating the digital data of the spatialpositions of the grid mark images in relation to the digital data of theobject images by reference to the camera position in relation to boththe grid marks image and the object image; and displaying the digitizedobject image on a computer-controlled visual display device; andmensurating the displayed image in a scale calibrated by the computerwith respect to the digitized reseau grid marks image.
 2. The method ofclaim 1, wherein the step of removing the grid marks from the capabilityof the camera to view them includes the step of removing theillumination of the grid marks.
 3. The method of claim 2, including thestep of providing the reseau in the form of a transparent plate withgrid marks in the form of grooves formed in its surface that ispositioned on the object, said grooves being formed with surfaces thatreflect and diffract light rays traveling longitudinally through saidtransparent plate to travel transversely to the surface of thetransparent plate that is opposite the grid mark grooves and into thecamera means, and providing a side light adjacent a peripheral edge ofthe transparent plate for directing light rays longitudinally throughsaid transparent plate to illuminate said grid marks.